Import gcc-dg/vect directory from GCC

[mablinov]

Hi all.

This works builds directly off of our other MR waiting to be merged here, and simply adds the gcc-dg/vect subfolder.

Under x86_64 there are 2913 build targets, 1152 passing tests.

There is a minor "hack" right now in that the original vect.exp file from upstream uses lots of glob patterns to create the list of tests to run - I've re-created this behaviour here by instrumenting the GCC vect.exp to echo the globs, cat'ted them into a file, and then copied that into a new file created by this MR called SingleSource/Regression/C/gcc-dg/vect/DgVectTestList.txt. This file is then consumed in SingleSource/Regression/C/gcc-dg/vect/CMakeLists.txt to figure out what tests to run/not run.